CIDH Pile: End Bearing/Skin Friction
CIDH Pile: End Bearing/Skin Friction
(OP)
I have a building design I'm working on, I'm asking the geotechnical engineer for soil design parameters and he is giving me the same end bearing numbers as he is for shallow footings:
Structural Loads
Axial Load (D+L+EQ)=100 kips
Moments (D+L+EQ)=25 ft kips
Shear (D+L+EQ)=15 kips
Preliminary Caisson/CIDH Pile size
24" diameter
15' deep
Soil Data:
Cemented Sandstone
Blow Count: 50 to 60 per foot
Density: 120 pcf
Allowable Bearing for shallow footings with 2' min. embed=3500 psf, 4500 psf with 3' min.
1. The geotech is not letting me use skin friction and end bearing at the same time, is this the standard of practice?
2. Shouldn't the end bearing value go up as the foundation gets deeper?
3. What are typical values for skin friction, is 40 psf/ft of depth in the ballpark, as in it increases with depth?
4. I know the skin friction mobilizes at a lower strain than does bearing, but are they typically combined, why or why not...?
much appreciated
Structural Loads
Axial Load (D+L+EQ)=100 kips
Moments (D+L+EQ)=25 ft kips
Shear (D+L+EQ)=15 kips
Preliminary Caisson/CIDH Pile size
24" diameter
15' deep
Soil Data:
Cemented Sandstone
Blow Count: 50 to 60 per foot
Density: 120 pcf
Allowable Bearing for shallow footings with 2' min. embed=3500 psf, 4500 psf with 3' min.
1. The geotech is not letting me use skin friction and end bearing at the same time, is this the standard of practice?
2. Shouldn't the end bearing value go up as the foundation gets deeper?
3. What are typical values for skin friction, is 40 psf/ft of depth in the ballpark, as in it increases with depth?
4. I know the skin friction mobilizes at a lower strain than does bearing, but are they typically combined, why or why not...?
much appreciated





RE: CIDH Pile: End Bearing/Skin Friction
RE: CIDH Pile: End Bearing/Skin Friction
RE: CIDH Pile: End Bearing/Skin Friction
RE: CIDH Pile: End Bearing/Skin Friction
2.End bearing depend on the shear strength etc of soil soit's increasing as deep of foundation increasing
3.Analytically, the skin friction value are different for shallow foundation and deep foundation
4.We can neglected the skin or end bearing capacity value if to small into account of bearing capacity
RE: CIDH Pile: End Bearing/Skin Friction
Consider 3.5 to 4 ft diameter to bring the end bearing pressures lower.
The 40 psf/ft sounds a lot like a Active equivalent earth pressure & not passive or skin friction value. Why not ask the geotechnical for passive and then use your IBC formula?
RE: CIDH Pile: End Bearing/Skin Friction
RE: CIDH Pile: End Bearing/Skin Friction
I've only seen discussions of skin friction and end bearing in the FHWA pile design manual, I'm waiting for the engineer's results on what he will allow for the skin friction and/or end bearing.
33 ksf is way to big, but wouldn't 12 or 15 ksf be a reasonable allowable end bearing pressure at 15 to 20 feet deep?
RE: CIDH Pile: End Bearing/Skin Friction
You will need to add strong language in the construction specs that Cobbles and difficult drilling would be encountered.
If the geotechnical engineer's parameters are super low, you may need to load test to failure and then use 50% of that values for design.